1. Field of the Invention
The present invention relates generally to an antenna device having an array antenna comprised of a plurality planar antennas, and more particularly to such an antenna device having a high antenna efficiency.
2. Description of the Related Art
Japanese Patent Laid-open Publication No. HEI 8-97620 discloses a multiple-beam planar array antenna comprised of a plurality of patch antennas (planar antennas) arranged over one surface of a dielectric substrate, a feeder part or unit, and feeder lines connecting the feeder unit and the individual patches antennas. The patch antennas are arranged so as to form a plurality of antenna parts each of which radiates beams of different tilt angles that are determined depending on the differences in length of the feeder lines connected to the individual patch antennas. The feeder lines are provided with a feed selecting means for selectively starting and stopping the feed of radio frequency energy to each of the antenna parts. The feed selecting means is composed of a plurality of selectively switchable PIN diodes.
In the disclosed antenna device, however, since the patch antennas (planar antennas) are arranged in the form of a matrix or rectangular array, the adjacent planar antennas tend to cause interference during transmission and reception of electromagnetic waves, thereby lowering the antenna efficiency (radiating efficiency) of the antenna device.